Constipation in Newborn

My newborn (2 weeks) has a hard time having a bm. I know it's normal for them to not go for days to weeks but he's in pain. He's breastfed. I'm taking vert pn dha prenatal vitamins which I couldn't take when I was pregnant bc it would cause constipation. Has anyone else had anything similar or know of any ideas to help him? I don't want to do rectal stimulation more than once or twice a day and this only relieves him temporarily. What can I do to make his stool softer?